1. Field of the Invention
The present invention relates to a mask structure for X-ray exposure for use in the manufacture of ICs, LSIs and the like, and an X-ray exposure device using this mask structure.
2. Related Background Art
In recent years, the development of X-ray exposure devices has been energetic with the increase of the density of LSIs and the like. Most of the X-ray mask structures for X-ray exposure are of such a permeable type as shown in FIG. 2. In general, a mask support 2 is formed from a material having a high X-ray permeability and a high mechanical strength on a mask supporting frame 1 comprising silicon single crystal, and an X-ray absorber pattern 3 of gold, tungsten or the like is further formed thereon. All of these members are mounted on a retaining frame 4.
An exposure system using such a mask structure is called a proximity system in which exposure is carried out maintaining a distance between the mask and a wafer at about 30-50 .mu.m. In this system, a stage is moved from one image to a next image to be exposed after the distance between the mask and the wafer is spread to about 150 .mu.m in order to prevent the mask from hitting against the wafer and breaking, and afterward the distance between the mask and the wafer is adjusted to 30-50 .mu.m again for the sake of the next exposure.
However, the X-ray mask support 2 is required to support the X-ray absorber pattern 3 and to have a high X-ray permeability, and therefore a film having a high mechanical strength and made of silicon nitride, silicon carbide or the like is self-supportingly used, with the thickness of the film being about 2 .mu.m. Therefore, when the distance between the mask and the wafer is changed at the movement of the stage from one image to the next region to be exposed in accordance with the proximity system, a pressure fluctuation occurs, so that pressure is applied to the mask support 2, with the result that the mask support 2 is bent inconveniently. In this case, a maximum bend quantity of the mask support 2 is as much as 10 .mu.m, and so a time of about 0.1 to 1 second is taken to relieve the bend.
Furthermore, when the mask support is electrified during the exposure, the mask support 2 bends similarly, as in the above case.
If the exposure is carried out with the mask support 2 being bent, a print error of the pattern takes place inconveniently.
Additionally, in an X-ray exposure device of a type in which the exposure is carried out setting the wafer and the mask vertically to the ground, chucking deviates owing to the gravity forces on the mask structure and other external factors sometimes, and in the worst case, the mask falls and breaks.